/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
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 *
 *
 *
 *
 *
 *
 *
 */

package java.io;


import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * Reads text from a character-input stream, buffering characters so as to
 * provide for the efficient reading of characters, arrays, and lines.
 *
 * <p> The buffer size may be specified, or the default size may be used.  The
 * default is large enough for most purposes.
 *
 * <p> In general, each read request made of a Reader causes a corresponding
 * read request to be made of the underlying character or byte stream.  It is
 * therefore advisable to wrap a BufferedReader around any Reader whose read()
 * operations may be costly, such as FileReaders and InputStreamReaders.  For
 * example,
 *
 * <pre>
 * BufferedReader in
 *   = new BufferedReader(new FileReader("foo.in"));
 * </pre>
 *
 * will buffer the input from the specified file.  Without buffering, each
 * invocation of read() or readLine() could cause bytes to be read from the
 * file, converted into characters, and then returned, which can be very
 * inefficient.
 *
 * <p> Programs that use DataInputStreams for textual input can be localized by
 * replacing each DataInputStream with an appropriate BufferedReader.
 *
 * @author Mark Reinhold
 * @see FileReader
 * @see InputStreamReader
 * @see java.nio.file.Files#newBufferedReader
 * @since JDK1.1
 */

public class BufferedReader extends Reader {

  private Reader in;

  private char cb[];
  private int nChars, nextChar;

  private static final int INVALIDATED = -2;
  private static final int UNMARKED = -1;
  private int markedChar = UNMARKED;
  private int readAheadLimit = 0; /* Valid only when markedChar > 0 */

  /**
   * If the next character is a line feed, skip it
   */
  private boolean skipLF = false;

  /**
   * The skipLF flag when the mark was set
   */
  private boolean markedSkipLF = false;

  private static int defaultCharBufferSize = 8192;
  private static int defaultExpectedLineLength = 80;

  /**
   * Creates a buffering character-input stream that uses an input buffer of
   * the specified size.
   *
   * @param in A Reader
   * @param sz Input-buffer size
   * @throws IllegalArgumentException If {@code sz <= 0}
   */
  public BufferedReader(Reader in, int sz) {
    super(in);
    if (sz <= 0) {
      throw new IllegalArgumentException("Buffer size <= 0");
    }
    this.in = in;
    cb = new char[sz];
    nextChar = nChars = 0;
  }

  /**
   * Creates a buffering character-input stream that uses a default-sized
   * input buffer.
   *
   * @param in A Reader
   */
  public BufferedReader(Reader in) {
    this(in, defaultCharBufferSize);
  }

  /**
   * Checks to make sure that the stream has not been closed
   */
  private void ensureOpen() throws IOException {
    if (in == null) {
      throw new IOException("Stream closed");
    }
  }

  /**
   * Fills the input buffer, taking the mark into account if it is valid.
   */
  private void fill() throws IOException {
    int dst;
    if (markedChar <= UNMARKED) {
            /* No mark */
      dst = 0;
    } else {
            /* Marked */
      int delta = nextChar - markedChar;
      if (delta >= readAheadLimit) {
                /* Gone past read-ahead limit: Invalidate mark */
        markedChar = INVALIDATED;
        readAheadLimit = 0;
        dst = 0;
      } else {
        if (readAheadLimit <= cb.length) {
                    /* Shuffle in the current buffer */
          System.arraycopy(cb, markedChar, cb, 0, delta);
          markedChar = 0;
          dst = delta;
        } else {
                    /* Reallocate buffer to accommodate read-ahead limit */
          char ncb[] = new char[readAheadLimit];
          System.arraycopy(cb, markedChar, ncb, 0, delta);
          cb = ncb;
          markedChar = 0;
          dst = delta;
        }
        nextChar = nChars = delta;
      }
    }

    int n;
    do {
      n = in.read(cb, dst, cb.length - dst);
    } while (n == 0);
    if (n > 0) {
      nChars = dst + n;
      nextChar = dst;
    }
  }

  /**
   * Reads a single character.
   *
   * @return The character read, as an integer in the range 0 to 65535 (<tt>0x00-0xffff</tt>), or -1
   * if the end of the stream has been reached
   * @throws IOException If an I/O error occurs
   */
  public int read() throws IOException {
    synchronized (lock) {
      ensureOpen();
      for (; ; ) {
        if (nextChar >= nChars) {
          fill();
          if (nextChar >= nChars) {
            return -1;
          }
        }
        if (skipLF) {
          skipLF = false;
          if (cb[nextChar] == '\n') {
            nextChar++;
            continue;
          }
        }
        return cb[nextChar++];
      }
    }
  }

  /**
   * Reads characters into a portion of an array, reading from the underlying
   * stream if necessary.
   */
  private int read1(char[] cbuf, int off, int len) throws IOException {
    if (nextChar >= nChars) {
            /* If the requested length is at least as large as the buffer, and
               if there is no mark/reset activity, and if line feeds are not
               being skipped, do not bother to copy the characters into the
               local buffer.  In this way buffered streams will cascade
               harmlessly. */
      if (len >= cb.length && markedChar <= UNMARKED && !skipLF) {
        return in.read(cbuf, off, len);
      }
      fill();
    }
    if (nextChar >= nChars) {
      return -1;
    }
    if (skipLF) {
      skipLF = false;
      if (cb[nextChar] == '\n') {
        nextChar++;
        if (nextChar >= nChars) {
          fill();
        }
        if (nextChar >= nChars) {
          return -1;
        }
      }
    }
    int n = Math.min(len, nChars - nextChar);
    System.arraycopy(cb, nextChar, cbuf, off, n);
    nextChar += n;
    return n;
  }

  /**
   * Reads characters into a portion of an array.
   *
   * <p> This method implements the general contract of the corresponding
   * <code>{@link Reader#read(char[], int, int) read}</code> method of the
   * <code>{@link Reader}</code> class.  As an additional convenience, it
   * attempts to read as many characters as possible by repeatedly invoking
   * the <code>read</code> method of the underlying stream.  This iterated
   * <code>read</code> continues until one of the following conditions becomes
   * true: <ul>
   *
   * <li> The specified number of characters have been read,
   *
   * <li> The <code>read</code> method of the underlying stream returns
   * <code>-1</code>, indicating end-of-file, or
   *
   * <li> The <code>ready</code> method of the underlying stream
   * returns <code>false</code>, indicating that further input requests
   * would block.
   *
   * </ul> If the first <code>read</code> on the underlying stream returns
   * <code>-1</code> to indicate end-of-file then this method returns
   * <code>-1</code>.  Otherwise this method returns the number of characters
   * actually read.
   *
   * <p> Subclasses of this class are encouraged, but not required, to
   * attempt to read as many characters as possible in the same fashion.
   *
   * <p> Ordinarily this method takes characters from this stream's character
   * buffer, filling it from the underlying stream as necessary.  If,
   * however, the buffer is empty, the mark is not valid, and the requested
   * length is at least as large as the buffer, then this method will read
   * characters directly from the underlying stream into the given array.
   * Thus redundant <code>BufferedReader</code>s will not copy data
   * unnecessarily.
   *
   * @param cbuf Destination buffer
   * @param off Offset at which to start storing characters
   * @param len Maximum number of characters to read
   * @return The number of characters read, or -1 if the end of the stream has been reached
   * @throws IOException If an I/O error occurs
   */
  public int read(char cbuf[], int off, int len) throws IOException {
    synchronized (lock) {
      ensureOpen();
      if ((off < 0) || (off > cbuf.length) || (len < 0) ||
          ((off + len) > cbuf.length) || ((off + len) < 0)) {
        throw new IndexOutOfBoundsException();
      } else if (len == 0) {
        return 0;
      }

      int n = read1(cbuf, off, len);
      if (n <= 0) {
        return n;
      }
      while ((n < len) && in.ready()) {
        int n1 = read1(cbuf, off + n, len - n);
        if (n1 <= 0) {
          break;
        }
        n += n1;
      }
      return n;
    }
  }

  /**
   * Reads a line of text.  A line is considered to be terminated by any one
   * of a line feed ('\n'), a carriage return ('\r'), or a carriage return
   * followed immediately by a linefeed.
   *
   * @param ignoreLF If true, the next '\n' will be skipped
   * @return A String containing the contents of the line, not including any line-termination
   * characters, or null if the end of the stream has been reached
   * @throws IOException If an I/O error occurs
   * @see java.io.LineNumberReader#readLine()
   */
  String readLine(boolean ignoreLF) throws IOException {
    StringBuffer s = null;
    int startChar;

    synchronized (lock) {
      ensureOpen();
      boolean omitLF = ignoreLF || skipLF;

      bufferLoop:
      for (; ; ) {

        if (nextChar >= nChars) {
          fill();
        }
        if (nextChar >= nChars) { /* EOF */
          if (s != null && s.length() > 0) {
            return s.toString();
          } else {
            return null;
          }
        }
        boolean eol = false;
        char c = 0;
        int i;

                /* Skip a leftover '\n', if necessary */
        if (omitLF && (cb[nextChar] == '\n')) {
          nextChar++;
        }
        skipLF = false;
        omitLF = false;

        charLoop:
        for (i = nextChar; i < nChars; i++) {
          c = cb[i];
          if ((c == '\n') || (c == '\r')) {
            eol = true;
            break charLoop;
          }
        }

        startChar = nextChar;
        nextChar = i;

        if (eol) {
          String str;
          if (s == null) {
            str = new String(cb, startChar, i - startChar);
          } else {
            s.append(cb, startChar, i - startChar);
            str = s.toString();
          }
          nextChar++;
          if (c == '\r') {
            skipLF = true;
          }
          return str;
        }

        if (s == null) {
          s = new StringBuffer(defaultExpectedLineLength);
        }
        s.append(cb, startChar, i - startChar);
      }
    }
  }

  /**
   * Reads a line of text.  A line is considered to be terminated by any one
   * of a line feed ('\n'), a carriage return ('\r'), or a carriage return
   * followed immediately by a linefeed.
   *
   * @return A String containing the contents of the line, not including any line-termination
   * characters, or null if the end of the stream has been reached
   * @throws IOException If an I/O error occurs
   * @see java.nio.file.Files#readAllLines
   */
  public String readLine() throws IOException {
    return readLine(false);
  }

  /**
   * Skips characters.
   *
   * @param n The number of characters to skip
   * @return The number of characters actually skipped
   * @throws IllegalArgumentException If <code>n</code> is negative.
   * @throws IOException If an I/O error occurs
   */
  public long skip(long n) throws IOException {
    if (n < 0L) {
      throw new IllegalArgumentException("skip value is negative");
    }
    synchronized (lock) {
      ensureOpen();
      long r = n;
      while (r > 0) {
        if (nextChar >= nChars) {
          fill();
        }
        if (nextChar >= nChars) /* EOF */ {
          break;
        }
        if (skipLF) {
          skipLF = false;
          if (cb[nextChar] == '\n') {
            nextChar++;
          }
        }
        long d = nChars - nextChar;
        if (r <= d) {
          nextChar += r;
          r = 0;
          break;
        } else {
          r -= d;
          nextChar = nChars;
        }
      }
      return n - r;
    }
  }

  /**
   * Tells whether this stream is ready to be read.  A buffered character
   * stream is ready if the buffer is not empty, or if the underlying
   * character stream is ready.
   *
   * @throws IOException If an I/O error occurs
   */
  public boolean ready() throws IOException {
    synchronized (lock) {
      ensureOpen();

            /*
             * If newline needs to be skipped and the next char to be read
             * is a newline character, then just skip it right away.
             */
      if (skipLF) {
                /* Note that in.ready() will return true if and only if the next
                 * read on the stream will not block.
                 */
        if (nextChar >= nChars && in.ready()) {
          fill();
        }
        if (nextChar < nChars) {
          if (cb[nextChar] == '\n') {
            nextChar++;
          }
          skipLF = false;
        }
      }
      return (nextChar < nChars) || in.ready();
    }
  }

  /**
   * Tells whether this stream supports the mark() operation, which it does.
   */
  public boolean markSupported() {
    return true;
  }

  /**
   * Marks the present position in the stream.  Subsequent calls to reset()
   * will attempt to reposition the stream to this point.
   *
   * @param readAheadLimit Limit on the number of characters that may be read while still preserving
   * the mark. An attempt to reset the stream after reading characters up to this limit or beyond
   * may fail. A limit value larger than the size of the input buffer will cause a new buffer to be
   * allocated whose size is no smaller than limit. Therefore large values should be used with
   * care.
   * @throws IllegalArgumentException If {@code readAheadLimit < 0}
   * @throws IOException If an I/O error occurs
   */
  public void mark(int readAheadLimit) throws IOException {
    if (readAheadLimit < 0) {
      throw new IllegalArgumentException("Read-ahead limit < 0");
    }
    synchronized (lock) {
      ensureOpen();
      this.readAheadLimit = readAheadLimit;
      markedChar = nextChar;
      markedSkipLF = skipLF;
    }
  }

  /**
   * Resets the stream to the most recent mark.
   *
   * @throws IOException If the stream has never been marked, or if the mark has been invalidated
   */
  public void reset() throws IOException {
    synchronized (lock) {
      ensureOpen();
      if (markedChar < 0) {
        throw new IOException((markedChar == INVALIDATED)
            ? "Mark invalid"
            : "Stream not marked");
      }
      nextChar = markedChar;
      skipLF = markedSkipLF;
    }
  }

  public void close() throws IOException {
    synchronized (lock) {
      if (in == null) {
        return;
      }
      try {
        in.close();
      } finally {
        in = null;
        cb = null;
      }
    }
  }

  /**
   * Returns a {@code Stream}, the elements of which are lines read from
   * this {@code BufferedReader}.  The {@link Stream} is lazily populated,
   * i.e., read only occurs during the
   * <a href="../util/stream/package-summary.html#StreamOps">terminal
   * stream operation</a>.
   *
   * <p> The reader must not be operated on during the execution of the
   * terminal stream operation. Otherwise, the result of the terminal stream
   * operation is undefined.
   *
   * <p> After execution of the terminal stream operation there are no
   * guarantees that the reader will be at a specific position from which to
   * read the next character or line.
   *
   * <p> If an {@link IOException} is thrown when accessing the underlying
   * {@code BufferedReader}, it is wrapped in an {@link
   * UncheckedIOException} which will be thrown from the {@code Stream}
   * method that caused the read to take place. This method will return a
   * Stream if invoked on a BufferedReader that is closed. Any operation on
   * that stream that requires reading from the BufferedReader after it is
   * closed, will cause an UncheckedIOException to be thrown.
   *
   * @return a {@code Stream<String>} providing the lines of text described by this {@code
   * BufferedReader}
   * @since 1.8
   */
  public Stream<String> lines() {
    Iterator<String> iter = new Iterator<String>() {
      String nextLine = null;

      @Override
      public boolean hasNext() {
        if (nextLine != null) {
          return true;
        } else {
          try {
            nextLine = readLine();
            return (nextLine != null);
          } catch (IOException e) {
            throw new UncheckedIOException(e);
          }
        }
      }

      @Override
      public String next() {
        if (nextLine != null || hasNext()) {
          String line = nextLine;
          nextLine = null;
          return line;
        } else {
          throw new NoSuchElementException();
        }
      }
    };
    return StreamSupport.stream(Spliterators.spliteratorUnknownSize(
        iter, Spliterator.ORDERED | Spliterator.NONNULL), false);
  }
}
